cianfa72's latest activity
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This is easy to address. Photon counting arguments are risky because not all states preserve photon number. A better approach is to... -
cianfa72 reacted to Ibix's post in the thread High School Why is the constant speed of light so unique? with
Like.
As A.T. says, the speed of sound is constant with respect to the medium. In air it's about ##330\mathrm{ms^{-1}}##, but if you are... -
cianfa72 reacted to A.T.'s post in the thread Undergrad Question about Parallel Transport with Like.
"Extrema" is a generalization of "minima" and "maxima" only, and doesn't include "saddles" which are "stationary" but not "extremal"...
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cianfa72 replied to the thread Undergrad Question about Parallel Transport.Ah ok, so you (mistakenly) thought you had found a (counter) example consisting of a geodesic of ##E^4## which is not a geodesic of the...
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cianfa72 reacted to A.T.'s post in the thread Undergrad Question about Parallel Transport with
Agree.
'Extremal' doesn't include saddles, like the longer part of a great circle. The safe statement for an arbitrary long geodesic is that... -
cianfa72 replied to the thread Undergrad Do existing EFE solutions support Closed Timelike Curves?.Ok, therefore, according the today standard physics, there is no way to take a CTC journey or reach some (remote) region of spacetime...
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cianfa72 replied to the thread Undergrad Do existing EFE solutions support Closed Timelike Curves?.Do physicists think that Gödel or Kerr-Gödel-type solutions could be plausible models for our Universe ?
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cianfa72 replied to the thread Undergrad Question about Parallel Transport.Ok, this is actually an example of the other way around. Namely geodesics of that 3-sphere's contained surface fail to be a geodesics of...
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cianfa72 replied to the thread Undergrad Do existing EFE solutions support Closed Timelike Curves?.Well, then, for instance in Gödel's universe, by following a suitable timelike path, one could came back to the event where the journey...
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cianfa72 posted the thread Undergrad Do existing EFE solutions support Closed Timelike Curves? in Cosmology.Hi, I'm curious about the following: taking the point of view of the standard physics of spacetime including EFE's solutions, are there...
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cianfa72 reacted to PAllen's post in the thread Undergrad Question about Parallel Transport with Like.
I am not sure that is always true. Consider, by analogy, a 3-sphere embedded in Euclidean 4 space. It can contain a geodesic of the...
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cianfa72 reacted to PAllen's post in the thread Undergrad Question about Parallel Transport with Like.
I am saying this is not necessarily true. True is that you can find a hypersurface containing it such it is a geodesic of the...
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cianfa72 replied to the thread Undergrad Question about Parallel Transport.No, maybe I wasn't clear. For any geodesic of the 4D Euclidean space you can always find an hypersurface containing it (on this...
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cianfa72 replied to the thread Undergrad Question about Parallel Transport.This raises the following point. Let's take a spacelike geodesic of the 4D Lorentzian spacetime. There exists a spacelike hypersurface...
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cianfa72 replied to the thread Undergrad Question about Parallel Transport.You mean, taking a spacelike hypersurface (endowed with the induced metric) is basically a recipe to build a 3D Riemannian manifold.